This application claims the priority benefit of Taiwan application serial no. 88115623, filed Sep. 10, 1999.
1. Field of Invention
The present invention relates to a pressure control device. More particularly, the present invention relates to a pressure control device for controlling the flow of ink from the ink reservoir of an ink cartridge.
2. Description of Related Art
Most conventional inkjet printers employ a jet nozzle to deliver ink to paper. The ink required by the print head is usually supplied from an ink reservoir within an ink cartridge. To direct the ink from the reservoir to the print head so that printing can be carried out smoothly, the How of ink must be regulated. Although regulating the flow of ink can guarantee a spray of fine ink drops, some mechanism must be present to prevent ink from leaking from the cartridge when the print head is not printing.
To prevent ink leakage, two self-adjusting mechanisms have been developed so far. The first method is the placement of some polymer foam inside the ink reservoir. Utilizing the capillary action of narrow spacing within the foam, leakage is prevented. However, storage capacity for this kind of ink reservoir is rather limited. The second method is to set up a sub-atmospheric or negative pressure inside the ink reservoir when the print head is not in use. A negative pressure is created when the ink reservoir is in a partial vacuum so that its internal pressure is lower than external atmospheric pressure. Hence, an increase in negative pressure means that the degree of vacuum inside the reservoir is increased. By setting up a negative pressure inside the ink reservoir, seepage of ink from the print head virtually stops.
Although the presence of a negative pressure inside the ink reservoir may suppress ink leakage from the print head, too much negative pressure will also prevent ink drops from getting out of the print head during printing. Moreover, if the external pressure changes, the negative pressure inside the reservoir needs to be changed correspondingly. For example, if there is a drop in the external pressure, the negative pressure must drop correspondingly in order to prevent the leakage of ink from the print head.
In 1980, Epson developed a type of ink reservoir described in U.S. Pat. No. 4,422,084. The invention uses organic polypropylene to form the ink reservoir. Negative pressure inside the ink reservoir is regulated by a set of springs both inside and/or outside the reservoir. However, using this type of pressure control mechanism, a portion of the ink inside the reservoir cannot be used. Furthermore, the ink reservoir is detached from the cartridge of the print head.
In 1982, Hewlett Packard has developed a type of ink reservoir for print heads described in U.S. Pat. No. 4,509.062. The invention relies on non-linear springs and a rubber bladder for maintaining a negative pressure inside the ink reservoir. One end of the spring is fixed upon a supporting structure while the other end is attached to the rubber bladder. However, due to the springs and other support structures, the volume of ink held by each reservoir in a multi-reservoir ink cartridge, for color printing especially, is severely limited.
In 1992, Hewlett Packard has developed another type of ink reservoir described in U.S. Pat. No. 5,757.706. A spring formed by a pair of thin plates is placed inside the ink reservoir. Through the forces exerted by the spring plates on two non-elastic soft walls of the reservoir, a suitable negative pressure is created. However, since the spring plates are enclosed inside the ink reservoir, the spring plates are likely to react chemically with the ink.
Accordingly, one object of the present invention is to provide a pressure control device for controlling the flow of ink from a print head cartridge. A negative pressure of suitable magnitude is formed inside the ink reservoirs where the ink is stored. Therefore, ink drops can exit the reservoir during a normal printing operation and cannot leak out from the reservoir when the printing stops. Furthermore, because the pressure control device enables the ink reservoirs to be fully compressed, even the last few drops of ink inside the ink reservoir can be used.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a pressure control device suitable for a multi-reservoir ink cartridge. The pressure control device employs an external traction spring means between the ink reservoirs of the cartridge. Each ink reservoir has at least a side surface formed from a flexible non-elastic material. When the ink reservoirs are full, the traction spring means is in a relaxed state. By withdrawing a small quantity of ink from each ink reservoir, atmospheric pressure exerts a force on the ink reservoirs leading to a small contraction. The resulting distortion of the traction spring means produces a force that resists further contraction of the reservoirs. Since the pressures inside the reservoirs are smaller than external atmospheric pressure, a back-pressure that prevents any ink from leaking out of the reservoirs is created. Through proper design of the traction spring means loading and elasticity of the ink reservoirs, a suitable ink jet is formed during normal printing operation. In addition, a pressure plate can be added to the traction spring means to squeeze ink from the reservoir more evenly. Hence, the back-pressure of each ink reservoir can be more effectively controlled and every drop of ink inside each ink reservoir can be fully utilized.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.